224 
SECOND REPORT - 1832 . 
recently published some good observations on a boring near 
Berlin *. The temperature of the earth, measured by that of 
deep-seated and copious springs, has conducted to a similar re¬ 
sult ; for their variation of temperature as connected with lati¬ 
tude is confined within smaller limits than the mean temperature 
of the air, indicating a proper temperature of the earth, which 
at the mean depth of springs diminishes that of those near the 
equator, and increases it near the poles ; the mean point, or 
where the ordinary temperature of the earth and that of the 
air are the same, being about latitude 56°. Von Buch pointed 
out some years ago this interesting factf, which was deduced 
from his own observations and those of others, especially of 
Wahlenberg in Sweden j. The question has lately been treated 
in its greatest generality by M. Kupffer, who has established 
to a considerable extent the course of what he calls the iso- 
geothennal lines, and has given formulae for their computation 
as well for longitude as latitude ; for, like Humboldt’s isother¬ 
mal lines, he finds that they do not regularly follow the parallels 
of latitude, but are subject to anomalous inflections. The form 
of the expression given by M. Kupffer is 
a — b sin 2 l—t, 
a and b being constants which vary with the meridian of the 
place, and which he has computed for a range extending from 
85° W. to 60° E. of Paris ||. Near the equator, the ground at 
25 metres depth appears to have a temperature 2° R. below the 
mean temperature of the air, whilst in Lapland it is as much 
above it. I do not think that the connexion of this remarkable 
fact with the proper temperature of the globe has been pointed 
out with sufficient distinctness, but this is not the place to insist 
upon it more particularly. 
It is obvious that the temperature of the ocean which covers 
so large a portion of the surface of our globe, must have a great 
influence in the modification of its climate. This subject has 
therefore occupied particular attention. The most active obser¬ 
vers have been Humboldt, Scoresby, Parry, Ross, Sabine, Hall, 
Davy, and Duperrey. The variations of temperature of the 
sea being comparatively small, the climate is subject to much 
smaller fluctuations than on continents. As might be expected, 
the maximum temperature of the air is greater than that of the 
surface water ; the mean temperature however, it appears from 
* Poggendorff’s Annalen, xxii. 146. 
f See the Edinburgh New Philosophical Journal, vi. 166 
X Wahlenberg’s observations were originally published in Gilbert's Annalen 
der Physik. || Voyage au Mont Elbrontz. 
